A bistable vertical coupling device described in EP Patent 2015145 meets the definition of the device given in the field of the invention. This device is provided for alternately starting and then stopping a chronograph mechanism. It includes for such purpose a switching mechanism including a coupling wheel permanently coupled to an output wheel, a coupling cone associated with a control member, a spring exerting an axial force between the first wheel and a plate forming a stop, a central tube for joining the plate to the assembly formed of the coupling wheel and the coupling cone, and finally a joint allowing friction coupling of said assembly to an input wheel.
The switching mechanism is actuated axially (i.e. perpendicularly to the respective planes of the input wheel and of the output wheel) by a control mechanism, which includes a clamp with two fingers, carrying, at their respective free ends, portions that each have an oblique surface for pressing laterally on the coupling cone (which consequently defines an uncoupling cone), and a column wheel which is driven step-by-step into a plurality of angular positions by means of an actuation device, notably a push-piece actuatable by the timepiece user. This column wheel actuates the clamp, in collaboration with a strip-spring, to alternately lift the assembly formed of the coupling wheel and the coupling cone against the axial force of the spring and uncouple the chronograph mechanism and remove the lateral pressure on this assembly in order to couple the chronograph mechanism, this coupling being achieved by the spring and the friction joint.
As is clear from the description above, the vertical coupling device of EP2015145 is relatively complex. Firstly, it requires a spring incorporated in the switching mechanism. Next, it occupies a lot of space in the general plane of the movement and it has quite a large height, due to the superposition of several elements, particularly of the coupling cone, the spring and the stop-plate. Finally, the control mechanism is not easy to fabricate and then assemble inside the timepiece movement.